1. Field of the Invention
The present invention provides methods of inducing cell cycle arrest and/or cell growth inhibition, with the methods comprising administering to the cells an effective dose of a compound of the present invention.
2. Background of the Invention
Prostate cancer is the most common malignancy, and second leading cause of cancer related deaths in men in the western world. Despite advances in screening and treatment of localized disease, advanced prostate cancer, to date, remains incurable.
It is well-established that androgens play a vital role in the development, growth, and progression of prostate cancer. Therefore, androgen deprivation therapy (ADT) remains the standard treatment for advanced prostate cancer. Current ADT includes treatment with luteinizing hormone releasing hormone (LHRH) agonists and/or androgen receptor (AR) antagonists. Unfortunately, agonists fail to inhibit release of adrenal androgens and AR antagonists have been shown to act as partial agonists in prostate cancer cells expressing mutated and/or over-expressed AR. See Chen C. D., ez al., Nat. Med., 10(1):33-9 (2004) and Fuse H, et al., Prostate, 67(6):630-7 (2007), which are incorporated by reference.
An alternative strategy for ADT is the global inhibition of androgen synthesis. This can be accomplished through the inhibition of the enzyme 17α-hydroxlase-C17,20-lyase (CYP17) which catalyzes the last two reactions in the production of androgens. The imidazole anti-fungal agent, ketoconazole, which is a non-specific cytochrome P450 inhibitor, has been used for prostate cancer treatment and has shown modest efficacy in patients no longer responding to anti-androgen treatment. See Small E. J., et al., J. Urol., 157(4):1204-7 (1997) and Trachtenberg J., et al., J. Urol., 130(1):152-3 (1983), which are incorporated by reference.
Ketoconazole treatment is, unfortunately, limited by its toxicity due to the lack of specificity for CYP17. Specific CYP17 inhibitors, however, are emerging as a promising new class of anti-prostate cancer agents. One such CYP17 inhibitor, abiraterone (17-(3-pyridyl)androsta-5,16-dien-3β-ol), has entered Phase II clinical trials where it has demonstrated efficacy in castration refractory prostate cancer patients. The inventors have discovered that VN/124-1, and structurally related CYP17 inhibitors, including abiraterone, are capable of inhibiting the growth of androgen independent cell lines, such as PC-3 and DU-145. The inventors also report the discovery that, unexpectedly, these CYP17 inhibitors induce the endoplasmic reticulum stress response (ERSR) as their mechanism of action with respect to growth inhibition. Importantly, these effects were seen at concentrations previously shown to be achievable in both plasma and within tumors in mouse prostate cancer xenograft models.
The endoplasmic reticulum (ER), which is a center of protein-folding within a cell, is extremely sensitive to disruptions in homeostasis, including disruptions in calcium concentrations. Such disruptions can induce the which also referred to as the unfolded protein response. The ERSR is an evolutionarily conserved pathway that seeks to relieve the build-up of unfolded proteins in the ER. To reduce levels of unfolded proteins in the cell, the cell first up-regulates ER-resident molecular chaperones such as glucose-regulated protein 78 (gp78/BiP), and reduces ER load through phosphorylation of the α subunit of the eukaryotic translation initiation factor 2 (eIF2α). Phosphorylation of eIF2α results in attenuation of translation of non-essential proteins, including growth related proteins such as cyclin D1 Though the ERSR is a survival pathway, prolonged stimulation of the ERSR results in growth arrest and apoptosis via the up-regulation of apoptotic-related proteins including the CCAAT/enhancer-binding protein homologous transcription factor (CHOP). As a result, the ERSR has been implicated in the anti-cancer activities of many synthetic and natural cancer therapeutics including clotrimazole, fatty acid synthase inhibitors, cox-2 inhibitors, 3131-diindolylmethane, and eicosapentaenoic acid.
We demonstrate that VN/124-1 induces the ERSR in cells resulting in the up-regulation of ERSR associated genes and the phosphorylation of eIF2α. This up-regulation of ERSR associated genes and phosphorylation of eIF2α leads to the inhibition of Cyclin D1 translation, which, in turn, results in G1 arrest of the cells. Analysis of intracellular calcium signaling reveals that VN/124-1 causes the release of Ca2+ from the ER resulting in the depletion of ER calcium stores, and a sustained rise in intracellular Ca2+ concentrations ([Ca2+]i).
Accordingly, VN/124-1 and related compounds hold promise for use in methods for arresting cells during cell cycle and inhibiting cell proliferation. Such methods may be employed in treating patients that have conditions associated with abnormal cell proliferation, such as cancer.